It is recognized that sufficient downforce must be exerted on a planter row unit to ensure the desired furrow depth and soil compaction is achieved. If excessive downforce is applied, especially in soft or moist soils, the soil may be overly compacted which can affect the ability of germinating seeds to break through the soil. If insufficient downforce is applied, particularly in hard or dry soil, the planter may ride up and out of the soil resulting in insufficient depth of the furrow.
In the past, coiled springs extending between the parallel arms of the row units of the planter were often employed to provide the additional or “supplemental” downforce needed to ensure the desired furrow depth and soil compaction was achieved. By positioning the spring at various preset locations along the parallel arms, the amount of downforce exerted on the row unit could be increased or decreased. However, the amount of supplemental downforce exerted by the spring remained constant until the spring was repositioned. For example, when the planter encountered hard or dry soil such that greater supplemental downforce is necessary to maintain furrow depth or the desired soil compaction, the operator had to stop and adjust the location of the spring in order to increase the supplemental downforce. Furthermore, during operation, as the seed or fertilizer in the hoppers was dispensed, the weight of the row unit gradually decreased causing a corresponding reduction in the total downforce on the gauge wheels, because the supplemental downforce exerted by the spring remained substantially constant until the spring was manually repositioned.
More advanced supplemental downforce systems, such as disclosed in U.S. application Ser. No. 12/679,710 (Pub. No. US2010/0198529) by Sauder et al. (hereinafter “the Sauder '710 Application”), which is incorporated herein in its entirety by reference, measure the strain in a member of the gauge wheel adjusting mechanism to determine the force being exerted against the gauge wheels to determine the downforce. However, central control systems that apply a common supplemental downforce to each row unit often fail to respond to unique loads experienced by each row unit, such that insufficient or excessive supplemental downforce may be applied to any given row unit.
Thus, there is a need for a downforce control system that effectively maintains a desired downforce at each row unit of an agricultural implement having a plurality of row units.